1. ITEC 224 Database Programming
Using SQL in PL/SQL
ITEC 224 Database Programming

2. Cursors used for SQL statements
Whenever an SQL command is executed in a PL/SQL block, Oracle assigns a private work area for that statement.
This work area contains information about the SQL statement and the set of data returned or affected by that statement.
There are two types of SQL cursor:
implicit cursor. The implicit cursor is used by Oracle server to test and parse the SQL statements
explicit cursor : the explicit cursors are declared by the programmers.

3. Attributes of Implicit Cursors
Using the implicit cursor, we can test the outcome of SQL statements in PL/SQL blocks using the following attributes:
SQL%ROWCOUNT: return the number of rows affected;
SQL%FOUND : BOOLEAN attribute indicating whether the recent SQL statement matches to any row;
SQL%NOTFOUND: BOOLEAN attribute indicating whether the recent SQL statement does not match to any row;
SQL%ISOPEN: a BOOLEAN attribute and always evaluated as FALSE immediately after the SQL statement is executed.

4. DML Commands
DML commands (insert/delete/update) are used with no change inside any PL/SQL block
Insert/delete/update commands modify the contents of the table and they do not really “return” any data.
It is possible to check the status of the statement using the implicit cursor attributes

5. DML commands Task: Insert a new row into the following table:
Author(AuthorId, Lname, FName)
BEGIN
INSERT INTO Author(AuthorId, Lname, FName)
VALUES(‘5266’, ‘Armanfar’, ‘Hamed’);
END;

6. DML commands Task: Append “old_” to the beginning of all last names
UPDATE Author
SET lname = ‘old_’ || lname;
DBMS_OUTPUT.PUT_LINE(SQL%rowcount || ’ names modified’);
END;

7. Use of DML commands
You can use as many DML commands as you need in one block
You should plan the DML commands and use the DCL commands commit or rollback in the appropriate places in your PL/SQL block.

8. Use of DML and DCL commands together
Employees.department_id%TYPE
Anchored declaration may be used here. v_dept_id has the same data type as the department_id column of the employees table
Use of DML and DCL commands together
Task:
Increase salary of all employees in a given department by 10%.
Read the department id from the keyboard.
If any rows were updated, insert a new row into the raises table containing the department id of the specified department and the number of rows modified and commit.
Otherwise undo the update.
Use the following tables:
DECLARE
v_dept_id number(4) :=&did;
v_count number;
BEGIN
UPDATE employees
SET salary = salary * 1.1
WHERE department_id = v_dept_id;
IF SQL%FOUND THEN
v_count := SQL%ROWCOUNT;
INSERT INTO raises
VALUES(v_dept_id, v_count);
COMMIT;
ELSE
ROLLBACK;
END IF;
END;
SQL%ROWCOUNT>0
Alternatively, rowcount may be used as part of the conditionIf the update command did not find any rows , t means rowcount=0.
Employees(employee_id, last_name, salary, department_id)
Raises(department_id, number_modified)

9. Use of SELECT in PL/SQL blocks
Select statement returns a set of results and these results are normally displayed on screen
When used inside a PL/SQL block, the results returned by the SELECT statement must be saved into variables therefore SELECT INTO statement is used
Syntax of Select Into :
SELECT <column list> INTO <variable list>
FROM <table list>
WHERE <conditions for choosing rows>
GROUP BY <columns | expressions to form group>
HAVING <conditions for choosing groups>
ORDER BY <columns | expressions to order the results>

10. Example Select Into
Task: Print on screen the average salary of all employees
Employees(employee_id, last_name, salary, department_id)
DECLARE
v_avg_salary employees.salary%TYPE;
BEGIN
SELECT avg(salary) INTO v_avg_salary
FROM employees;
DBMS_OUTPUT.PUT_LINE(
‘The average salary of all employees is ’ ||v_avg_salary);
END;
The average salary of all employees is

11. Example Select Into DECLARE v_name employees.last_name%TYPE; BEGIN
Task: Print on screen names of employees in the employees table.
Employees(employee_id, last_name, salary, department_id)
DECLARE
v_name employees.last_name%TYPE;
BEGIN
SELECT last_name INTO v_name
FROM employees;
DBMS_OUTPUT.PUT_LINE( ‘Employee name is ’ ||v_name);
END;
If select into returns more than one row, an exception (error) is raised and the program crashes.
DECLARE *
ERROR at line 1:
ORA-01422: exact fetch returns more than requested number of rows
ORA-06512: at line 4

12. Example Select Into
Task: Print on screen name of employees in department 99
DECLARE
v_name employees.last_name%TYPE;
BEGIN
SELECT last_name INTO v_name
FROM employees;
WHERE department_id = 99;
DBMS_OUTPUT.PUT_LINE( ‘Employee name is ’||v_name);
END;
If select into returns no rows, an exception (error) is raised and the program crashes.
DECLARE *
ERROR at line 1:
ORA-01403: no data found
ORA-06512: at line 4

13. Handling Select Into exceptions
NO_DATA_FOUND : A SELECT INTO statement returns no rows, or your program references a deleted element in a nested table or an uninitialized element in an index-by table.
TOO_MANY_ROWS : A SELECT INTO statement returns more than one row.VALUE_ERRORAn arithmetic, conversion, truncation, or size-constraint error occurs. For example, when your program selects a column value into a character variable, if the value is longer than the declared length of the variable, PL/SQL aborts the assignment and raises
VALUE_ERROR. In procedural statements, VALUE_ERROR is raised if the conversion of a character string into a number fails.

14. DML related Exceptions
Every error that can be detected by Oracle has a unique number. Some exceptions have pre-defined names associated with them.
Oracle Exception Name
Oracle Error Number
Description
NO_DATA_FOUND
ORA-01403
SELECT INTO statement returns no rows
TOO_MANY_ROWS
ORA-01422
SELECT INTO statement returns more than one row.
VALUE_ERROR
ORA-06502
An arithmetic, conversion, truncation, or size-constraint error occurs
ZERO_DIVIDE
ORA-01476
Attempt to divide a number by zero.
DUP_VAL_ON_INDEX
ORA-00001
Uniqueness of a column is violated by INSERT or UPDATE

15. Handling exceptions of Select Into
DECLARE
v_name employees.last_name%TYPE;
v_deptid employees.department_id%TYPE := &dept_id
BEGIN
SELECT last_name INTO v_name
FROM employees;
WHERE department_id = v_deptid;
DBMS_OUTPUT.PUT_LINE( ‘Employee name is ’||v_name);
EXCEPTION
WHEN TOO_MANY_ROWS THEN
DBMS_OUTPUT.PUT_LINE(‘ More than one row’);
WHEN NO_DATA_FOUND THEN
DBMS_OUTPUT.PUT_LINE(‘ No data’);
END;
There are no employees in department 99
Exception handling section
Enter value for dept_id: 99
old 3: v_deptid employees.department_id%TYPE := &dept_id
new 3: v_deptid employees.department_id%TYPE := 99
No data
PL/SQL procedure successfully completed.

16. Handling exceptions of Select Into
DECLARE
v_name employees.last_name%TYPE;
v_deptid employees.department_id%TYPE := &dept_id
BEGIN
SELECT last_name INTO v_name
FROM employees;
WHERE department_id = v_deptid;
DBMS_OUTPUT.PUT_LINE( ‘Employee name is ’||v_name);
EXCEPTION
WHEN TOO_MANY_ROWS THEN
DBMS_OUTPUT.PUT_LINE(‘ More than one row’);
WHEN NO_DATA_FOUND THEN
DBMS_OUTPUT.PUT_LINE(‘ No data’);
END;
There are two employees in department 20
Exception handling section
Enter value for dept_id: 20
old 3: v_deptid employees.department_id%TYPE := &dept_id
new 3: v_deptid employees.department_id%TYPE := 20
More than one row
PL/SQL procedure successfully completed.

17. Handling exceptions of Select Into
DECLARE
v_name number;
v_deptid employees.department_id%TYPE := &dept_id
BEGIN
SELECT last_name INTO v_name
FROM employees;
WHERE department_id = v_deptid;
DBMS_OUTPUT.PUT_LINE( ‘Employee name is ’||v_name);
EXCEPTION
WHEN VALUE_ERROR THEN
DBMS_OUTPUT.PUT_LINE(‘Data type conversion problem’);
WHEN OTHERS THEN
DBMS_OUTPUT.PUT_LINE(‘error’);
END;
There is only one employee in department 10
OTHERS is a catch-all phrase for exceptions
Enter value for dept_id: 10
old 3: v_deptid employees.department_id%TYPE := &dept_id
new 3: v_deptid employees.department_id%TYPE := 10
Data type conversion problem
PL/SQL procedure successfully completed.

18. SELECT INTO CAN HANDLE ONLY A SINGLE ROW

19. Handling exceptions of Select Into
DECLARE
v_name varchar2(2);
v_deptid employees.department_id%TYPE := &dept_id
BEGIN
SELECT last_name INTO v_name
FROM employees;
WHERE department_id = v_deptid;
DBMS_OUTPUT.PUT_LINE( ‘Employee name is ’||v_name);
EXCEPTION
WHEN VALUE_ERROR THEN
DBMS_OUTPUT.PUT_LINE(‘Data type conversion problem’);
WHEN OTHERS THEN
DBMS_OUTPUT.PUT_LINE(‘error’);
END;
There is only one employee in department 10 and his last name is Whalen
OTHERS is a catch-all phrase for exceptions
Enter value for dept_id: 10
old 3: v_deptid employees.department_id%TYPE := &dept_id
new 3: v_deptid employees.department_id%TYPE := 10
Data type conversion problem
PL/SQL procedure successfully completed.

20. Handling exceptions of DML statements
BEGIN
INSERT INTO regions
(region_id, region_name)
VALUES(1, ‘SCT’);
EXCEPTION
WHEN DUP_VAL_ON_INDEX THEN
DBMS_OUTPUT.PUT_LINE(‘Region_id must be unique’);
WHEN OTHERS THEN
DBMS_OUTPUT.PUT_LINE(‘Error’);
END;
Region_id is the Primary key of regions table and therefore must be unique. Region_id=1 already exists in the table
Region_id must be unique
PL/SQL procedure successfully completed.

21. You should anticipate all possible problems and handle them in the exception handling section

22. Summary This week we covered Cursors Cursor Attributes
How to use DML commands in PL/SQL blocks
How to use select INTO in PL/SQL blocks
Handling exceptions related to SELECT INTO and DMLcommands
Next Week we will learn about the explicit cursors